1. Field of the Invention
This invention relates to a dicing apparatus for microelectric circuit fabrication such as semiconductor integrated circuits or large scale integrated circuits in which a wafer is separated into individual small-dimensioned die.
2. Description of the Prior Art
Generally, there are three types of the dicing apparatus: diamond scribing, laser scribing, and a diamond wheel sawing type. The diamond wheel sawing type cuts the wafer using a rotating diamond dicing blade. In order to cut precisely, the dicing blade has a very sharp circular edge in the range of 10-30 .mu. thickness and rotates at very high speeds in the range of 20,000-30,000 revolutions per minute. The dicing blade is formed as a very thin disk having a hole at the center and is fitted on a rotating spindle, being held between two flanges.
Furthermore, the dicing apparatus has a cooling system which pours coolant against a cutting interface. Water sprayed from a coolant nozzle is usually used as a coolant to: first lower the temperature at the face; second provide lubrication between the cutting edge and the wafer; and finally, clean the cutting debris away from the cutting area. Prior art devices have the disadvantage that the debris causes damage to the wafer or die being cut.
FIGS. 1a and 1b show prior art dicing apparatus using a dicing blade. Referring to FIGS. 1a and 1b, a dicing blade 1 is held by flanges 201 and 202 from both sides of the dicing blade, the flanges being fitted on a spindle 12, and fixed by a nut 14. Coolant nozzles 3 are connected to a coolant pipe from which cooling water 7 is sprayed and flows in a direction 8 because of the rotation of flanges 201 and 202 and blade 1. A wafer 4 is cut along a dicing path along which the wafer 4 is separated into dice. Bonding pads 61 and 62 on each dice are for the bonding of a lead wire during the process of die assembling. The wafer is mounted on a platform 9 for cutting. The arrow 20 indicates the direction of rotation dicing blade 1, and the arrow 21 indicates the running direction of the rotating spindle 12.
There are two cutting modes when the dicing blade saws the wafer: one is a up-cut mode and the other is a down-cut mode. FIG. 1a shows the dicing apparatus working in the down-cut mode, and if the direction of 20 or 21 is reversed, the cutting mode would be changed to an up-cut mode. Usually these two cutting modes are used to save time in the cutting process by running the dicing blade back-and-forth on the wafer. However, when the dicing blade works in the down-cut mode, much of the cutting debris hits the surface of the wafer with the cooling water splashed by the rotating flange causing damage to the bonding pads on the wafer.
The surface of the wafer 4 is coated with a coating material such as a silicon dioxide or phospho-silicate glass to protect the fabricated microelectronic circuit on the wafer from damage and dirt. However, the coating material can not be applied on the bonding pads and the dicing paths, because the bonding pads are for bonding the lead wires and the dicing paths are for cutting the water.
Above all, the bonding pads are very delicate, because they are made of the metal like aluminum, so the cutting debris easily is driven into them. If so, poor bonding or an increase in the connection resistance will occur after bonding. This has been a serious problem because it deteriorates the quality and reliability of the fabricated semiconductor die.
The problems in the prior art will be explained further in FIGS. 2a and 2b. FIG. 2a is a diagram of the areas around the cutting interface using the dicing apparatus of the prior art. FIG. 2b is also a diagram of the same cutting interface especially showing the flow of the cooling water being sprayed against the cutting interface. In the figures, reference numerals having the same numerals to FIGS. 1a and 1b indicate the same objects.
As shown in FIG. 2a, in the dicing apparatus of the prior art, the flanges 201 and 202 are made so that each flange becomes thinner to decrease the weight of the flanges in order to maintain the high speed rotation of the dicing blade. The width (t.sub.1) at the circumference of the flange edge is in the range of 200-300 .mu.m, and an angle (.theta..sub.1) between tapered side-surface of the dicing blade is in the range of 10-17 degrees. On the other hand, each bonding pad is usually positioned so that the distance from the center of the dicing path 5 to the center of the bonding pad is approximately 100 .mu.m. Consequently, as shown in FIG. 2b, the cooling water 7 from the coolant nozzle 3 is sprayed at the tapered side-surface of the flange 201 or 202 and flows along the tapered side-surface of the flange due to the centrifugal force of the flange rotation. The water flow 8 illustrates this. Therefore, the cooling water violently hits the bonding pads 61 or 62 and acts like a hammer, so that the water drives the cutting debris, which are on the bonding pad, into the bonding pad, or the water carries the cutting debris and drives them into the bonding pad 61 or 62. This has been a serious problem in the fabrication of microelectronic dice by dicing apparatus using the dicing blade of the prior art.